Tire pressure depends on what you're doing. I know trials riders like to run low pressures, but they also run really fat tires (like 3" I think) to make up for it. When you are doing lots of spins high pressures are the way to go, lots of freestyle riders like 60-100lbs in their tires.
You can do a proper bunny hop on a mountain bike, just keep at it. I'm not great at bunny hops but on my Specialized Enduro I can get 24" on a good day, with a hardtail I can go higher. Learning to manual your bike will help with the bunny hops as well, it helps you get a feel for getting the front end up without hopping.